W211 Fuse Box - need fuse which is live only with ignition

[Noddy 99]

Hi, chaps,

I've bought a fuse tap kit so that I can hard-wire my phone to charge/display every time the ignition is on.

However, every fuse I've tried to piggyback to in the fuse box by the steering wheel is permanently live - obviously that's going to drain my battery as I leave the phone in the car, permanently connected.

The reason why I've had to try every fuse is that the supplied fuse box diagram bears no relation to reality. On other threads people have suggested using either the cigarette lighter or the rear wiper. BUT THERE IS NO SUCH FUSE IN MY CAR... :-(

Go easy with me - I know nothing about electrical terminology...

Many thanks.

 

[Blobcat]

The 12v socket should be ignition switched live, if you can’t find the fuse (it will be there) you could tap into the power at the back of the 12v socket

 

[Noddy 99]

Hi,

Thanks for your help.

On the Mercedes fuse list, it has "socket load compartment", "socket rear" and "socket trunk"; nothing about the socket in the front console... :-(

I know the socket is working because I've wired some LED footwell lights into it. I haven't the faintest idea where its fuse is, though...

 

[Blobcat]

Hi,

Thanks for your help.

On the Mercedes fuse list, it has "socket load compartment", "socket rear" and "socket trunk"; nothing about the socket in the front console... :-(

I know the socket is working because I've wired some LED footwell lights into it. I haven't the faintest idea where its fuse is, though...

Use one of those fuses you’ve found, they should also be ignition switched

 

[Noddy 99]

Good call but they're located in the boot... :-(

 

[mercmancdi]

Have you heated seats at no 40 fuse , you are in side panel where you open the door I assume, it should be ignition operated, if no heated seats fitted it may be blank avaible to use. I used fuses in that box before that were ignition linked. Have you a simple tester just to run through them with ignition off see what ones don’t light.

 

[EmilysDad]

does the fuse box you've found not have a power supply on the side that you can use. A fuse box in my car has some ignition live & some permanently live.
This is for a Smart ... but the principle is the same ... you'd need an account to see it all, but you can see enough to get the gist. https://www.evilution.co.uk/mod/sam-fuse-holder.htm?highlight=fuse holder
And this is a pre-wired fuse holder .... https://www.smart-stuff.parts/brown-fuse-holder-permanent-live---sam-unit-r5r6r7r8r9 No idea why it's priced as it is!!!! But Merc sell them, you have to wired them up yourself.

Just realised the fuse carrier is for a box of 1000 ....

This is the one ... they used to sell them pre-wired https://www.smart-stuff.parts/black-fuse-holder

 

[Noddy 99]

mercman, that's a good shout, actually. The car's in the garage for a separate issue at the moment so I've asked the guy to have a look at it. If he draws a blank, I'll try your suggestion. Cheers.

 

[RhodieBill]

Should be FUSE 54 under the Bonnet Driver's side Fuse Box.

 

[Noddy 99]

does the fuse box you've found not have a power supply on the side that you can use. A fuse box in my car has some ignition live & some permanently live.
This is for a Smart ... but the principle is the same ... you'd need an account to see it all, but you can see enough to get the gist. https://www.evilution.co.uk/mod/sam-fuse-holder.htm?highlight=fuse holder
And this is a pre-wired fuse holder .... https://www.smart-stuff.parts/brown-fuse-holder-permanent-live---sam-unit-r5r6r7r8r9 No idea why it's priced as it is!!!! But Merc sell them, you have to wired them up yourself.

Just realised the fuse carrier is for a box of 1000 ....

This is the one ... they used to sell them pre-wired https://www.smart-stuff.parts/black-fuse-holder

Thanks for the referrals. I'm just going to wait for the garage man's verdict. I might actually go for the box of 1000 - I'd have enough fuse-holders to last forever!

 

[Noddy 99]

Should be FUSE 54 under the Bonnet Driver's side Fuse Box.

How do you route a cable into the engine bay, though? Not something I've ever done...

 

[RhodieBill]

How do you route a cable into the engine bay, though? Not something I've ever done...

Throttle Cable or Wiring Harness Grommet???

 

[Noddy 99]

Update: the garage guy has gone all over the car with his multi-meter and says that ALL the fuses are reading as constant live.

This doesn't make rational sense so I think that the ACCESSORY circuits are on a timed delay. A multi-meter will read them as constant, even though they are actually switched.

Anyway, I'm sitting in my car now with no ignition and with my phone piggy-backed to the radio fuse. After 30 mins, we'll see if my theory is correct...

 

[Blobcat]

Update: the garage guy has gone all over the car with his multi-meter and says that ALL the fuses are reading as constant live.

This doesn't make rational sense so I think that the ACCESSORY circuits are on a timed delay. A multi-meter will read them as constant, even though they are actually switched.

Anyway, I'm sitting in my car now with no ignition and with my phone piggy-backed to the radio fuse. After 30 mins, we'll see if my theory is correct...

The radio has both a permanent and ignition switched live - first keeps the memories and settings, second switches it on when you turn the key.
It sounds like your garage man shouldn't be let loose with a multi-meter...

 

[Noddy 99]

Well I sat there for 40 minutes and the phone was still charging at the end. So with the ignition off and all the doors closed, my phone had been drawing power from the radio circuit...

I must admit - last night I tried pretty much every fuse in that cluster and they were all giving constant power...

 

[RhodieBill]

Hi. I have to say I've piggy-backed a feed off of the Fuse for the Cigarette Lighter on a few on these Mercs and not once has the Lighter Socket ever been permanently live...
Have you tried the Fusebox at the end of the Dash. You have to have the Door open to get to it? Should be on the Driver's side. I used a fuse in there a couple of times....

 

[spenttherent]

Don't you just move fuse 54 sideways to change from perminant live to ignition live ?

 

[Tony Dyson]

Don't you just move fuse 54 sideways to change from perminant live to ignition live ?

That's an interesting and useful facility and one I've never seen or heard of before, It doesn't exist on my W 204 but I can see the benefits of having it! 53 and 54 are allocated to "Trailer Hitching" on mine.

 

[Noddy 99]

Hi. I have to say I've piggy-backed a feed off of the Fuse for the Cigarette Lighter on a few on these Mercs and not once has the Lighter Socket ever been permanently live...
Have you tried the Fusebox at the end of the Dash. You have to have the Door open to get to it? Should be on the Driver's side. I used a fuse in there a couple of times....

That's exactly where I'm looking, Bill, but my line-up of fuses looks nothing like yours. All those 30amp green fuses are at the bottom of my layout, not the top. Also, according to the Mercedes fuse diagram that came with the car, there is no fuse identified for the front cigarette lighter...

Some people say it's fuse 54 under the bonnet but that's not in the fuse diagram. I'd prefer not to go under the bonnet as I'm convinced the routing will be a nightmare...

 

[spenttherent]

That's an interesting and useful facility and one I've never seen or heard of before, It doesn't exist on my W 204 but I can see the benefits of having it! 53 and 54 are allocated to "Trailer Hitching" on mine.

It did work on my 211 but I'm not sure now if it affected the front or the rear sockets